ROOTS 



105 



101. ROOTS 

 Object. To study plant foods. 



It is a well-known fact that plants will not thrive indefi- 

 nitely in the same soil : 



1. The plant takes up from the soil those substances 

 which it needs for its nourishment so that in time the soil 

 becomes impoverished through loss of the food elements 

 which it originally contained. 



2. The presence in the soil of harmful bacteria may render 

 it unfit for the growth of certain crops. 



3. The presence of poisonous excreta which have been 

 thrown off by previous crops. 



The loss of food content is by far the most important of 

 these causes of sterility of the soil. 



The farmer, the gardener, and the florist meet these condi- 

 tions in several ways. 



(a) Repotting and transplanting. When a plant shows 

 by its growth that it has exhausted the food supply in its 

 soil, it can be carefully removed from the flowerpot and 

 repotted into a larger one with a supply of fresh soil. It 

 can likewise be removed to another locality where the soil 

 has not become impoverished. But there is a better method 

 known as (6) fertilizing. 



A fertilizer is any substance which contains materials 

 suitable for plant food. They may be of mineral origin, 

 such as phosphate earth, lime, plaster, or Chile saltpeter; 

 or vegetable matter, such as decayed vegetation, wood 

 ashes, or green growth plowed under; or they may be 

 animal matter, such as bones, sea shells, guano, and waste 

 from stables. 



(c) Nutrient solutions are often made up, consisting of 



